GB1036740A - Brake adjuster - Google Patents

Abstract

1,036,740. Internal shoe drum brakes. BENDIX CORPORATION. June 17, 1965 [June 22, 1964 (2); July 8, 1964], No. 25714/65. Heading F2E. An automatic adjuster, arranged in association with each of a pair of wedge - type actuators of an internal shoe drum brake, of the kind in which a pair of shoes are arranged to anchor at their trailing ends in both directions of rotation, comprises, within the housing 32 of each actuator an internally threaded sleeve 40 rotatable in a bore in one of the plungers 34 of the wedge-operated unit, a screw 44 held against rotation through a stud 46, which is grooved to engage the adjacent shoe web and is attached by a spring clip 51 to the screw, and a pawl-andratchet arrangement, for automatically rotating the sleeve 40 to advance the screw 44, which includes a resilient connection adapted to yield under "knock-back" conditions, i.e. if the arrangement tends to make an adjustment during a brake application when the frictional force to be overcome is so high that damage to the pawl might result. In the embodiment shown, the resilient connection is provided by a hairpin type spring 72 arranged in a recess in the outer end of the sleeve 40, its head and the lower extremities of its legs being engaged within peripheral openings formed between flanges 58, 60 of a ring 42 and between corresponding flanges 54, 56 of the sleeve to couple the ring and sleeve together while permitting limited relative rotation in one direction against the force of the spring. The ring is provided with ratchet teeth 78 engaged by a pawl 80 pivoted at 82 to the actuator housing and urged towards the ring by a compression spring 86 (Fig. 3, not shown) located in a bore in the housing. In operation, when the brake is applied the plungers 34 and 36 are moved apart by the wedge 37 to act on the shoe webs 28, 30 via a slotted end 50 of plunger 36 and the stud 46, respectively, and if clearance is excessive the pawl will pivot sufficiently to slip one of the teeth 78 so that on subsequent brake release the ring is rotated and, since the screw 44 is no longer acted on by the braking force, the sleeve 40 is also rotated to effect adjustment. Should " knock-back " occur while the brakes are applied the hairpin spring 72 will be overcome and the ring will be rotated without rotating the sleeve. Should the brake then be released the hairpin spring will be enabled to turn the sleeve 40 so that full adjustment for wear is obtained although the return movement of plunger 34 is reduced. The flanges 54, 56 of the sleeve and the flanges 58, 60 of the ring 42 have grooved ends for co-operation with the spring 72 either as shown in Fig. 4 or as in Fig. 5 (not shown). The spring slip 51 attaching stud 46 to the screw 44 engages a series of notches 55 on the end of the screw which can be engaged by a tool for manual adjustment, the clip then slipping over the notches. The shoes have hold-down springs 24 secured to a torque plate 10 by springs 25 (Fig. 1, not shown). In another embodiment (Figs. 7-10, not shown), the hairpin spring is replaced by a resilient plate 160 which transmits the rotational torque between the ratchet ring and the sleeve 40 but under " kick-back " conditions distorts in the axial direction of the sleeve so that inward movement of the plunger does not pivot the pawl and therefore no rotational movement is imparted to the ring until the brake is released. In a further embodiment (Figs. 11-13, not shown) ratchet teeth are formed integrally with the sleeve 40 and the pawl is modified by the provision of a resilient connection between the stem 262 of the pawl 280 and a modified pivot pin 282 which is rotatable in the actuator housing, the resilient connection allowing the stem 262 to slide transversely of the pivot pin axis during kick-back conditions, so that no rotation is imparted to the sleeve 40.